1. Field of the Invention
This invention relates to a mobile crane comprising a chassis, which has at least two axles and on which a revolving superstructure is movably mounted by means of a slewing bearing consisting of an outer ring and an inner ring, also comprising a preferably telescopic boom, which is pivoted to the revolving superstructure and which is adapted to be supported on a supporting bracket of the crane in position for road travel, and also comprising a cabin for use during crane and road travel operations.
2. Description of the Prior Art
Mobile cranes of that kind can be operated in two modes, namely, in a travel mode, preferably road travel mode, and in a crane mode, in which the chassis is usually supported by extensible or hinged struts and the lifting and handling operations are performed in that the boom is pivotally moved and the superstructure is rotated. For these two modes of operation a cabin is required, which during road travel provides for the driver the required view over the road and which during crane operation permits a constant watching of the crane hook during the lifting and transporting operations. In order to meet said requirement, it is known to provide a mobile crane of the kind described first hereinbefore with two cabins, one of which is mounted on the chassis so that the driver has a good view over the road whereas the other cabin for use during crane operation is mounted on the revolving superstructure and faces the tip of the boom. But the provision of the two cabins for road travel and for crane operation, respectively, is expensive and adds to the cost of the crane truck. For this reason, mobile trucks have also been provided with a combined cabin for use during travel and crane operations.
In such known cranes comprising a single cabin for use during travel and crane operations, the cabin is mounted either on the chassis or on the rotating deck so as to face in the direction of the boom. If the cabin is mounted on the chassis the view permitted during crane operation will be inadequate in most positions of the revolving superstructure because the cabin does not follow the slowing movements.
On the other hand, if the cabin is mounted on the revolving superstructure, the view during travel operation will be greatly obstructed by the boom so that, as a rule, the mobile crane cannot be licensed under the motor vehicle construction and use regulation. Such cranes are known as slow-moving trucks for use on building sites or as rough-terrain cranes and for travel on the building site where the boom can slightly be raised so that the view will be improved. But such cranes cannot be licensed for general road travel.
It is also known to provide a mobile crane which is of the kind described first hereinbefore and has a double-purpose operator's cabin, which is mounted on the revolving superstructure. That double-purpose operator's cabin has for road travel a seat which permits the operator to view over the road in the direction which is opposite to the boom. For crane operation the operator occupies a second seat, which provides for the operator a view toward the tip of the boom. That combined cabin is very large and requires two control stations for road travel and crane operation, respectively.